Asthma (Acute)

Asthma Pathway (BTS, NICE, SIGN) [SIGN 244]

Article Last Updated:17/12/2025

Minor restructuring of the management section has been made to improve readability. No changes in actual content have been made.

Date: 02/12/25

Background Information

Definition

Asthma exacerbation: a typically reversible episode of lower airway obstruction (bronchospasm) characterised by an acute or subacute worsening of baseline symptoms and lung function in patients with asthma. In some cases, a patient may present for the first time in an exacerbation. ^[Ref]

Aetiology

Main causes of exacerbations include: ^[Ref]

Asthma triggers
- Viral URTIs
- Allergen exposure (e.g., pollen, fungal spores, food)
- Air pollution
- Weather changes
Poor adherence to ICS-containing medication

NB: Asthma exacerbations may occur in the absence of known risk factors / triggers

Clinical Features

Symptoms

Typical symptoms: ^[^Ref^]

Increasing breathlessness / wheeze / cough / chest tightness
Symptoms often occur at rest, disturb sleep or limit activity
Rapid progression / worsening

Signs

Typical auscultation findings:

Widespread expiratory polyphonic wheeze
Prolonged expiratory phase

Features seen in severe / life-threatening asthma (see the asthma attack severity for more details):

Severe asthma attack	Respiratory rate ≥25/min Pulse ≥110/min Inability to complete a sentence in one breath Increased work of breathing (e.g. use of accessory muscles, nasal flaring, tripod positioning, chest wall retractions, grunting) – not technically included as a severe feature
Life-threatening asthma attack	↓ SpO₂ Silent chest on auscultation Agitation, drowsiness, or confusion (ominous signs of impending respiratory failure) – life-threatening asthma feature

Investigations and Diagnosis

Acute asthma attack is a clinical diagnosis

The following tests are aimed at stratifying the severity:

↓ PEF (compared to personal best or predicted)
ABG – important if the patient is hypoxic
- Initial → respiratory alkalosis ± hypoxaemia
- Late → hypercapnia / respiratory acidosis

In asthma exacerbation, a normal / elevated / rising PaCO₂ is a red flag:

Normally, patients with acute asthma hyperventilate → low PaCO₂ (respiratory alkalosis)
If PaCO₂ is normal or rising, this means the patient’s respiratory muscles are fatiguing, airflow obstruction is worsening, and ventilatory failure is imminent.

Therefore, a normal PaCO₂ immediately makes it a life-threatening attack, and a raised PaCO₂ immediately makes it a near-fatal attack.

Although PEF is included in severity criteria for acute asthma, it is rarely performed in real-life emergency assessments. Acutely breathless patients often cannot generate a reliable reading, and immediate clinical stabilisation takes priority. In practice, clinicians stratify severity using clinical features (speech, respiratory rate, accessory muscle use, oxygen saturation), making PEF more of a textbook tool than a practical first-line assessment in acute attacks.

Prognosis

Favourable prognosis for most patients with rapid symptom resolution after acute management ^[Ref]
Relapse rate: ~7-15% after ED discharge
- History of prior exacerbations → Strongest predictor of future episodes
Poor prognostic indicators ^[Ref]
- History of prior severe exacerbations (esp. requiring hospitalisation/ICU admission)
- Poor baseline lung function
- Poor asthma control
- Inadequate ICS therapy (including poor adherence)
- Smoking

Complications

Main complication (severe/life-threatening exacerbations) → respiratory failure +/- acute respiratory acidosis

Adult Guidelines

Asthma Attack Severity

Severity	Criteria
Moderate	No features of severe acute asthma, and: PEF >50-75% (best or predicted) Increasing symptoms
Severe	Any of the following: PEF 33-50% (best or predicted) Respiratory rate ≥25/min Pulse ≥110/min Inability to complete a sentence in one breath – easiest way to see if a patient is having a severe (or worse) attack or not
Life-threatening	Any of the following: PEF <33% (best or predicted) SpO₂ <92% or PaO₂ <8 kPa Normal PaCO₂ (4.6-6.0 kPa) – indicates respiratory muscle fatigue Low pH Cyanosis Exhaustion or altered conscious level Arrhythmia or hypotension Silent chest
Near-fatal	Any of the following: PaCO₂ >6.0 kPa Requiring mechanical ventilation with raised inflation pressures

You can remember life-threatening features using the ‘33,92, CHEST’ mnemonic

33 → PEF <33%
92 → SpO₂ <92%
C → Cyanosis
H → Hypotension
E → Exhaustion / poor respiratory effort (normal PaCO₂)
S → Silent chest (poor air entry)
T → Tachycardia or bradycardia (arrhythmias)

Referral and Admission Criteria

ALL patients with severe asthma attacks and onwards (i.e. severe + life-threatening + near-fatal) needs referral to the hospital.

Admission criteria:

Life-threatening or near-fatal asthma attack
Severe features persist after initial treatment
Pregnant
Presentation at night
Asthma attack whilst being on oral corticosteroids
Previous near-fatal asthma attack

Management

Acute Management

Moderate Attack

Moderate asthma attacks can generally be managed in primary care, as an outpatient setting. Offer all the following:

β₂ agonist bronchodilator (e.g. salbutamol) via spacer
- If no improvement → nebulised salbutamol 5mg (preferably oxygen-driven)
Prednisolone 40-50mg (continue for a minimum of 5 days)

If the patient is not responding / worsening despite salbutamol (spacer and/or nebuliser) → refer to secondary care is necessary

Severe Attack Onwards

Severe attacks and onwards (including life-threatening and near-fatal) need to be managed in secondary care.

Initial therapy – offer ALL the following:

Oxygen therapy	Only offer oxygen if SpO₂ <94%
Bronchodilator therapy	Offer: Nebulised salbutamol 5mg (preferably oxygen-driven) +/- Nebulised ipratropium 0.5mg (usually given routinely if life-threatening attack or add-on if poor response to salbutamol)
Corticosteroid therapy	Oral prednisolone 40-50mg daily (continue for a minimum of 5 days), or If the patient cannot swallow oral tablets (e.g. due to vomiting) → IV hydrocortisone 400mg daily

Further therapy (only to be used under the direction of a senior medical staff):

Medical therapy	IV magnesium sulfate 1.2-2g over 20 min (single dose) IV aminophylline (no robust evidence) IV salbutamol (rarely used)
Ventilatory support	Transfer to ICU for intubation is indicated if there is: Hypercapnia Falling pH or rising hydrogen on ABG Persisting or worsening hypoxia Exhaustion, altered conscious state Poor respiratory effort or respiratory arrest

IV magnesium sulfate is commonly used in practice to manage severe / life-threatening / near-fatal asthma attacks, as it is a relatively safe drug and has robust evidence.

However, aminophylline and salbutamol (IV) are rarely used in practice, only considered in very refractory cases and under specialist care.

Unlike in COPD, non-invasive ventilation has NO ROLE in asthma. If medical management failed, escalation to ICU for intubation is necessary.

Monitoring Treatment

Measure the following to monitor treatment:

PEF
Pulse oximetry
Blood gas

Hospital Discharge

There is no explicit guidance on when to discharge, but the following should be met:

PEF >75% (best or predicted), and
Stable on medical therapy that can be continued at home (i.e. oral tablets, inhalers)

Actions to be performed before discharging the patient:

Provide asthma education
- Inhaler technique (check and advise on where appropriate)
- PEF record keeping
- Written PEF and symptom-based personalised asthma action plan

Follow up
- With GP within 2 days
- With respiratory clinic within 1 month

Children Guidelines

Asthma Attack Severity

Essentially the same as adults, apart from age-specific heart rate and respiratory rate, which have been removed for simplification.

The main difference is that SpO₂ <92% puts the patient in the severe category (in adults, SpO₂ <92% would put the patient in the life-threatening category)

Severity	Criteria
Moderate	No features of severe acute asthma, and: PEF >50-75% (best or predicted) Increasing symptoms
Severe	Any of the following: SpO₂ <92% PEF 33-50% (best or predicted) Inability to complete a sentence in one breath
Life-threatening	SpO₂ <92% + any of the following: PEF <33% (best or predicted) Silent chest Poor respiratory effort Confusion Cyanosis

Acute Management

The main difference regarding the acute management in children, compared to adults is the different prednisolone dose:

Adult: 40-50 mg for 5 days
Children: 3 days
- >5 y/o → 30-40 mg
- 2-5 y/o → 20 mg
- <2 y/o →up to 10 mg

Doses of IV hydrocortisone and magnesium should also be reduced.

Moderate Attack

Moderate asthma attacks can generally be managed in primary care / outpatient setting. Offer all the following:

β₂ agonist bronchodilator (e.g. salbutamol) via spacer
- If no improvement → nebulised salbutamol 5mg (preferably oxygen-driven)
Prednisolone (continue for a minimum of 3 days)
- >5 y/o → 30-40 mg
- 2-5 y/o → 20 mg
- <2 y/o →up to 10 mg

If the patient is not responding / worsening despite salbutamol (spacer and/or nebuliser) → referral to secondary care is necessary